Yes, a one second burst from a Phalanx will shred a speed boat, putting about 75 rounds per second down-range. The Phalanx has enough ammo for about 20 such bursts before its magazine is exhausted.
It then needs five minutes for the crew to swap in a fresh mag while they watch speed boats 21 thru 40 approaching.
a) the Phalanx is the only defensive weapon which will be brought to bear
b) the carrier won't make tracks at 30 knots away from the speedboats
c) speedboats 21-40 are going to be at *all* eager to continue pressing the assault after watching their friends being turned into a red mist to absolutely *NO* effect on the Americans.
Cheers!